This invention relates to the sortation of articles such as food products in accordance with the color of the product as compared to a reference standard while the article free falls through an illuminated inspection chamber.
The typical prior art color sorting apparatus utilizes a reference or background of predetermined reflectivity arranged in the same plane as a sensor which measures reflected light from both the background and the articles passing through the sorting apparatus. The reference level at which sortation takes place is determined by a comparison of light reflected from the article to the light reflected from the reference or background. When no product is in the optical plane of the sensor, the electrical condition of the sensor is returned to the level determined by the reference and all objects being sorted are measured from that level. Typically, a reference level is chosen from which desirable objects produce either no change or a change in condition of the circuitry opposite to the change produced by an undesirable object. As the color or reflectivity of the objects being sorted changes, it is quite often necessary to change the reference level to maintain the proper balance for correct sorting. Typically, this is done by replacing a reference background with a background of appropriate color or reflectivity for the objects being sorted. This method has the disadvantage, however, of requiring the selective use of several of the various references which are colored in steps or ranges. Further, the changing of the reference requires significant effort and time during which the sorting apparatus is not operating.
In another system for varying the reference level, the reference background may be moved toward or away from the light source so that the intensity of the light reflected from the background varies. Since light energy decreases as the square of the distance from the background, the system is not linear and therefore it is difficult to establish the proper reference level before effective sorting operations can commence.
Another approach known in the prior art is to vary the angle of the reference with respect to the plane of the sensor and the light source. This method is difficult to control since the position of the light source and the surface characteristics of the reference cause irregular nonlinear changes in the light directed to the sensor.
Further, in such sorting of articles, particularly food objects, the freefall trajectory of the article through the inspection port should be controlled to prevent the object from moving away from a predetermined path. As long as the apparatus is designed for use to inspect a specific product, the trajectory of that object can be planned for in the design of the apparatus. The resultant apparatus therefore is not conveniently adaptable to objects deviating from the characteristics of the object for which it is designed. Known prior art apparatus has not permitted convenient adjustment or control of the trajectory of an object through the inspection port to accommodate wet or dry objects or objects of different physical characteristics which affect their freefall trajectory.
Typically, articles which do not meet the desired standards are removed from the inspection chamber by means of a blast of fluid pressure from a nozzle. In the prior art, a nozzle directs a jet of fluid pressure, such as air, to strike and displace the object from the predetermined path in response to a signal from the detector. The positioning of the nozzle with respect to the path of the article is of extreme importance and if the nozzle and article are not in alignment then the jet of air cannot strike the article and the article will not be rejected.